Now these two IPs are both mine, the difference between them is the last three numbers. Those numbers are randomly (or maybe in some order) given to me when I connect the my ISP, and I don't think my ISP is the only one doing this. So my script part "protecting" visitors to vote twice really works only during one connection establishment.

So, what I would like to know is how I could shorten (is this BTW correct english?) the IP by removing everything after the last dot ("."). Then I could combine that with $ENV{'HTTP_USER_AGENT'} to get a working double voting protection, not prefect of course, but better than the one I have now.

I'm sorry to post this here if you think this a Beginner question.....

IP tracking for your purpose (or any other) has its limited usefulness. The example you gave of recieving different ips is perfect. You see there that you can merly dial up again and recieve a different ip (dynamic ips from an available pool that your isp has). This is extremly popular with isps because of the limited number of ips that the internet has currently available. There is another flip side to your delima with the ip as well. If you hang up and someone else at your isp dials up and gets your previously assigned ip then they will not be allowed to vote on this poll. Cookies too have their limitations. Simply put, if the person doesn't have cookies on or manually removes a cookie they can vote twice. If you want to do all you can to prevent stuffing your ballot box, I recommend a combination of the two processes. One, set a cookie if possible and check for this cookie when someone votes and two log ips with a time and set a time frame like 12 hours before that ip can vote. This is a popular method with many of the ad programs you see on the net to prevent padding of visits to a site or clickthroughs. I hope this helps in your efforts to prevent padding of your poll program.